Generally, a power converter is a power processing circuit that converts an input voltage or current source into a specified output voltage or current. Power converters are used in numerous types of applications including computers, audio/video equipment, mobile electronic devices, power systems, and the like.
One type of power converter, known as a DC/DC power converter, is operative to convert an input voltage waveform having a DC component into an output DC voltage 15 waveform which may be at a different voltage level than the input voltage waveform. For various reasons, it is often desirable for the input to be electrically isolated from the output of the power converter. To accomplish this, an isolation transformer may be used, which may the input DC voltage to be “chopped” into an AC voltage. Further, in order to perform the waveform conversion from an AC output of the isolation transformer to a DC 20 output voltage, rectification circuitry may be used. Traditionally, rectification circuitry included one or more diodes coupled to the secondary side of the isolation transformer. Since diodes only conduct current when they are forward biased, they may be used to convert the AC voltage from the isolation transformer to an output DC voltage. Alternatively, the rectification circuitry may include synchronous rectifiers that utilize transistor switches that are selectively turned on and off synchronous with the AC signal being rectified in order to control the conduction of current from the isolation transformer to the rectifier output.
The increasing computational speeds and densities of integrated circuits (ICs) have led to a reduction of their operating voltages. This reduction of operating voltages requires DC/DC converters to provide higher output current to achieve similar power output. As the output voltage is decreased and the output current is increased, the power loss incurred by the output rectifiers becomes a dominant factor for the efficiency of the power converter.
In order to allow the use of relatively small energy storage elements and filtering components (e.g., capacitors, inductors, transformers, and the like), the switching devices associated with the power converter may be switched at a relatively high frequency (e.g., a few hundred kilohertz). However, this high frequency switching may cause large voltage spikes and high frequency ringing at the output rectification circuitry. The voltage spikes and high frequency ringing may generally be caused by the parasitic or leakage inductance of the isolation transformer and the parasitic capacitance of the rectification diodes or transistor switches.
The voltage spikes and high frequency ringing are undesirable for several reasons. For example, the high voltage spikes may require the use of rectification devices that are rated for high voltages, which may be costly and larger in size. Further, the use of high voltage rated devices may reduce the efficiency of the power converter because those devices may have relatively high conduction losses. Additionally, the energy transmitted by the high frequency ringing and high voltage potentials may induce electromagnetic interference (EMI) problems in the various components of the power converter or other surrounding components.
To deal with this problem, various passive and active snubber or clamping circuits have been developed to compensate for the above-noted undesirable properties. These circuits generally have one or more shortcomings that may include increased costs and/or reduced efficiency of the power converter.
It is against this background that the energy recovery snubber circuits for power converters described herein have been invented.